Water permeable membranes may be used in a number of applications to provide desired separation of components. For example, dissolved substances such as salts can be separated from their solvents, e.g. water, by a procedure known as reverse osmosis. Reverse osmosis is an effective and versatile technology for water desalination. This technology can produce potable water from brackish and sea waters as well as surface, lake, and river waters in a one-step process after feed pretreatment. Thus, large volumes of usable water for industrial, agricultural, and home use can be produced from previously unusable water sources. In another example, water permeable membranes may be useful in dialysis and pervaporation.
Some water permeable membranes may be formed from a cross-linked aromatic polyamide interfacially polymerized on a porous support. See, U.S. Pat. No. 4,277,344, the disclosure of which is incorporated herein by reference. See also, U.S. Pat. Nos. 5,254,261, 5,246,587, 6,015,495, 6,063,278, and 6,245,234, the disclosures of which are also incorporated herein by reference. Although these water permeable membranes may have good performance including high salt rejection and good water flux, increased water flux, high salt rejection, or both is desirable.